Electrical control device



Dec. 11, 1951 N. HAMPTON ET AL 2,573,353 ELECTRICAL'CONTROL DEVICE Y Filed April 11, 1945 s Sheets-Sheet 1 LAL mu row Z614 Mild FIG. 2

IN ME N TORS ATTOPNE V r Dec. 1951 L. N. HAMPTON 'ETAL 2,578,353 ELECTRICAL CONTROL DEVICE Filed April 11, 1946 6 Sheets-Sheet s g I k,

Dec. 11, 195] [ml-{AMPTQN 2,578,353

ELECTRICAL, comm 1. DEVICE Filed April 11, 1946 v s Sheets-Sheet 4 L.N.HAMPTON INVENTORS O. $.A.ME$C/1' C. V. OBS T wmw A 7' TOR/Mfr Dec. 11, 1951 HAMPTON ETQL 2,578,353

ELECTRICAL CONTROL DEVICE Filed April 11, 1946 6. Sheets-Sheet 6 FIG /6 LJV. HAMPTON INVENTORS 0.-S.A.ME$CH ATTORNEY,

Patented Dec. 11, 1951 ELECTRICAL CONTROL DEVICE Leon N. Hampton, New York, Orwar S. A. Mesch, es V. Obst, Richmond. Hill,

St. Albans, and Charl N. Y... assignors to Bell T Incorporated, New York,

New York elephone Laboratories, N. Y., a corporation of Application April 11, 1946, Serial No. 661,246

6 Claims.

This invention relates to variable electrical control devices. and more particularly to variable electrical control devices suitable for use in electrical apparatus and systems in which precise electrical potentials are required.

In some cases the electrical apparatus employed in precision electrical systems: must be readily transportable and it is a desideratum that the control devices employed therein be. of relatively light weight. and compact construc-- tion.

The object of the invention is to provide an improved potentiometer of relatively light weight and compact construction and. suitable for use in precision electrical apparatus and systems.

A feature of the invention resides in a body of the potentiometer.

Another feature resides in means provided for holding an electrical resistance element in. required place in the body and for holding predetermined points of the resistance element against movement in the body.

Another feature resides in a collector ring structure and arrangement and associated parts.

Another feature resides in adjustable-supporting means for a wiper contact.

Other-features residing in the structures and arrangements of various members and parts in the potentiometer are pointed out and described inthe specification.

In the drawings;

Fig. 1 is a. top plan view of the potentiometer with part of a cover broken away topermit a view of-the interior ofthe potentiometer;

Fig. 2 is a side elevational view and partly; in section of the potentiometer;

Fig. 3 is a top plan view'of the body;

Fig. 4 is a view in cross-section of the bodyand taken on the line 4-4. in Fig. 3;

Fig. 5 isan under surface view of the body;

Fig. 6 is a view of a portionof Fig. 5 but with terminals mounted on the body and wires connected to the terminals and extending through apertures in the body;

Fig; '7 is an enlarged plan view; partly in section, ofa portion of thepotentiometer and lookingdownwardly in the potentiometer;

Fig. 8 is aside view, partly in section of aportion of the'potentiometer and taken on the line 8.8 in Fig. 7;

Fig. 9- is an enlarged cross-sectional view of a portion of the:potentiometerandtaken on the line 9-9 of Fig. '7 and shows a wedge-deviceholding aresistance element in required placein the body;

Fig. 10 is a view in cross-section of portions of the wedge. device: andportions of the body and resistance element and istaken on the line i10,ll3 in Fig. 7

Fig. 11, is a side elevational view of one. part of thewedge device;

Fig. 12- is a view in cross-section of the part shown in Fig. 11 and taken on the line [2-42 inthat figure;

Fig. 13 is a side elevational view of another part of the wedge device;

Fig. 14, is a view in cross-section of the part shown inFig. 13 and taken on the line [4-44 in that figure;

Fig.'15,is,a top-view, partly in section of aportion of the potentiometer andtaken on the line !5l5 in Fig. 8';

Fig- 16 is an enlarged view, in cross-section, of the adjustable supporting means for the wiper contact and takenon. the line lG-IB in Fig. 7;

Fig; 17' is an enlarged top view of a portion of the adjustable supporting means shown in Fig. 1.6 and taken on the; line ll-ll in Fig. 16 with certain parts removed;

Fig. 18 is an enlarged view in perspective of a spiral threaded adjustment member employed in the. adjustable; supporting means shown in Fig. 16; and

Fig. l9 is a View; partly in section, of a nut detail and. associated parts employed in. the adjustable supporting means shown in Fig. 16.

The potentiometer as shown in Figs. 1 and 2 comprises a body: lfii'anda cover llwhich cooperatively'form a housing for potential controlling parts of the potentiometer, the potential. controlling parts comprising wire wound resistance elements and. Wiper contacts operable in. frictionalengagement withv the resistance elements. The numberzof resistance elements and the number of wiper contacts .employedsin. the potentiometer are matters of. choice. and may bevaried as to. number and arrangement. to meet certain predetermined requirements.

For the purposezofi illustratingzand explaining the invention. and not-in: the sense of'a limitation. of the invention a. certainnumber of resistance'. elements andawiper contacts are shown and described and the body-v structure is such that it will accommodate the. resistance elements and Wiper contacts shown.

The body It. maybe made of any material found. suitable for the purpose butisshownin the. drawings. as being'made' of insulatingv material. In somecases, for instancawehavemade thebody or magnesium or. magnesium alloy and walls 50 of the recesses 49 being 53 of terminals such for instance as in other cases of thermoplastic material. The body l6 may be readily produced by molding or machine cutting a suitable material to the form and structure required or both molding and machine cutting operations may be employed in producingthe body l6.

The body I6 is of cup-like form and as shown in Fig. 4 comprises a centrally apertured lower base wall l8, an outer wall l9 and concentrically arranged spaced walls extending from the lower base wall H3. The number of concentric walls provided in the body |6 and extending into the space defined by the outer wall l9 may vary according to requirements and comprise as shown in Figs. 3 and 4 the walls 20, 2|, 22, 23, 24 and 25. The concentric walls in the body l6 extend upwardly in the body |6 to difierent heights and cooperate to define annular spaces 26, 21, 28, 29, 36, 3| and 32 in the body l6. The annular spaces 26 to 30, inclusive are closed at the bottom by the lower wall E8. The annular space 3| is open at the bottom and is in register with the annular space 32 but is separated from the space 32 by a horizontal wall 33 which joins the annular walls -24-and and forms a top wall for the space 3| and a lower wall for the space 32. The lower base wall it as shown in Fig. 3 is provided with ribs 34 which extend radially from the wall 24 to the wall 23 and across the lower portion of 'the space 30.

The outer wall IQ of the body |6 extends considerably' above the upper ends of the walls 20 to 25, inclusive to provide a relatively large space 35 in the upper portion of the body l6 for accommodation of certain parts of the potenti- 3 ometer. The outer wall IQ of the body I6 is increased in thickness about midway between theupper and lower ends of the wall l9 to form an integral annular shoulder 36 which serves as a stop for the lower end of the cover |1 when the cover. H is properly mounted on the body |6. Above the shoulder 36 the body I6 is provided with a male thread 31 which in cooperation with an internal thread 38 formed in the lower portionofthecover l1 serves to prevent accidental separation of. the cover H from the body l6. The lower end portion of the outer wall IQ of the body l6 extends beyond the lower surface of the lower wall [8 to form an annular skirt portion 39 which is externally threaded at 40 to provide means for securing the body l6 to a support, not shown.

The lower base wall N3 of the body |6 as shown in Figs. 4 and 5, is of stepped form comprising -concentric annular horizontal wall portions 4|, .42, 43, 44, and 46, the wall portion 4| being the highest in plane and each of the wall porctions next in order being in a lower plane than the immediately preceding wall portion. The wall portions 4| to 46 form closures for the lower ends of the annular spaces 26 to 30, respectively so that the base of each annular space is at a difierent level fromthe others. The lower surfaces of the annular horizontal wallportions 4| to 46 are recessed at spaced points to provide round recesses 41, rectangular recesses 48 and graduated depth recesses 49, the upper closure progressively and downwardly thickened at the points 5| and 52. The recesses 41 as shown in Figs. 6 and 8 are provided to accommodate mounting screws the terminal 54. I The rectangular recesses 48 are provided to serve in the nature of knockouts to permit ter- -min'als or relatively large gauge wires to be ex- The horizontal wall 33 which joins the annular walls 24 and 25 is provided with ribs 55 and spaced recesses 56, the recesses 56 being provided so that portions of the wall may be knocked out to allow the. extension of wires 51 through the wall 33. The recesses 56 are also provided with wing extensions 58 so that portions of the wall 33 may be knocked out in such form that a relatively flat sheet metal terminal, not shown, may be extended through the wall 33. The recesses 56 are also provided not only to facilitate the extending of terminals or wires through the wall 33 but also to accommodate as shown in Fig. 8 a flanged bushing 59, the purpose of which will be later explained.

The annular spaces 26 to 29, inclusive, are provided to accommodate resistance elements 60, 6|, 62 and 63, respectively as shown in Fig. 1, each resistance element being bent to follow in general the curvature of the predetermined annular wall in the body l6 and so that the resistance element will fit into the predetermined annular space in the body l6. The resistance elements shown in the illustrations of the potentiometer are wire wound cards each comprising as shown in Fig. 8 a card 64 and a plurality of turns of resistance wire 65 wound on the card 64. The material of the card 64 and the type of resistance wire wound on the card are matters of choice and each resistance element is set edgewise in a predetermined annular space in the body l6 and so that an upper edge 66 of the resistance element is slightly above the upper end of the annular space in which the resistance element is located.

The annular walls 20 to 25, inclusive, extend to difierent heights in the space defined by the wall H] of the body IS, the height of extension being greater for each annular wall in accordance with the distance each annular wall is from the longitudinal center of the body l6. The upper edges of the annular walls 26 to 23, inclusive are shouldered to provide ledges 61 and upwardly extending edge portions 6-8, the latter of which have spaced further upwardly extending lug portions 69 which may be used as reference points in adjusting the wire wound cards so that predetermined turns of resistance wire on the cards will be located at'required positions. A ledge '61 is also formed on the wall H! to correspond with the ledges 61 on the other annular walls abovementioned, the ledge 61 on the wall l9 being, however, considerably below the top of the wall IS.

The outer cylindrical surfaces of the walls 20 to 23, inclusive are recessed 'at space points to provide notches 10 which extend downwardly from the tops of the walls 25 to 23 to the lower wall IS. The notches 13 are tapered, being deeper at the top than at the lower ends. The

part F9 and the Wedge sticks 8i8|.

wall 19 is recessed at spaced points to provide divided seats 12 for arms of a spider not shown and not used in the particular potentiometer used herein as an illustration of the invention but used in certain other potentiometers following in general the structure of the one herein shown and described.

The wall 25 defines a space I13 through which a shaft 13 is extended, the shaft 13 being arranged so that relative rotation of the shaft 13 and the body [6 may be accomplished. In the upper end of the wall 25 a conical seat bearing 74 is provided to receive a conical bearing 15 on the shaft 73. An enlarged lower end portion 16 of the shaft 13 is journaled in a bearing 11 mounted in the lower end of the wall 25.

Each resistance element in the potentiometer must be precisely mounted in place in the body l6 and so that predetermined turns of resistance wire in each resistance element will be positioned at predetermined required points in the potentiometer and will not move from the required points when the potentiometer is operated or subjected to changes in temperature met in service.

The resistance elements 60, 6|, B2 and 63 after being placed edgewise in the annular spaces 26, 21, 28 and 29, respectively, in the body It are held in place and at predetermined required spaced points by means of wedge devices 18, each of which comprises a spring part 19 shown in Figs. 11 and 12, a channel part 86 shown in Figs. 13 and i l and two wedge sticks 8| shown in Fig; 10. l v

The spring part 19 as shown in Figs. 11 and 12 is in general of wedge type form and channel like in cross-section. Portions of theside walls 82 and 83 are extended outwardly to form flanges 84 and 85, respectively, which run lengthwise of the part 19. The side walls 82 and 83 are slit downwardly from the top for a portion of their length to create a tapered spring finger portion 86 which is curved away from the main portions of the side walls 82 and 83 and so that the top of the spring finger portion 86 is considerably spaced from the top of the main portion of the spring part [9. Lugs 8! and 88 are formed on the upper ends of the side walls 82 and 83, respectively and are bent inwardly toward each other to cooperatively form a partial closure for the top of the channel 89. Near the lower end of the spring part 19 a tongue an is formed and extended angularly from and beyond the main portion of the spring part 19. The lower end of the sprin part 79 is provided with an angularly extending The channel part 80 is, in general, of wedge type form and channel like in cross-section and is constructed and dimensioned so that it will accommodate the channel portion of the spring When the spring part it and the channel part 80 of the wedge device it are assembled and placed in the slot H in the body IS the side walls 92 and 93 of the channel part 86 are in parallel relation with the side walls of the slot 1|, the edges of the side walls 552 and 93 are in positions normal to the plane of the flanges 84 and 85, respectively, of the spring part 19 and the lower end of the channel part 86 rests on the foot 9! of the spring part 19. The tongue 99 on the spring part if) extends partially across the lower portion of the annular space in the body It in which the wedge device it happens to be located. The upper end or" the spring finger portion 86 i the spring part 19 bears against the inner surface of the back wall 94 of the channel part and the spring finger portion 86 will be pressed more or less toward the main portion of the spring part 79 in accordance with the space available for accommodation of the wedge device 78. The side walls 92 and 93 of the channel part 80 extend in spaced relation with the side walls 82 and 83, respectively, of the spring part 19. The wedge sticks Bi -8i are wedge shaped and may be driven downwardly in the spaces between the walls 82, 33 and the walls 92, 93 of the wedge device 18 to make the walls 92, 9-3 of the channel part 36 closely engage the corresponding side walls of the slot H. The length of the wedge sticks 8l-8l employed and the extent to which the Wedge sticks extend into the spaces between the parts 19 and 86 may vary in some cases but should be suflicient to cause the parts 79 and 80 to remain in the slot 15. One edge of the wedge stick BI is serrated as shown at 95 in Fig. 10. The serrations d5 are provided in the wedge stick 8! to make it relatively easy for an assembler of the parts to break off excess portions of the wedge stick 8| when the wedge stick 8! is longer than required.

The resistance elements 5-3 to 68, inclusive are all mounted in the body it in the same manner and are held in place in the body It by means of the wedge devices 13. A description of the placement and mounting of one of the resistance elements in the body it will therefore be sufficient for an understanding of how each resistance element is mounted in required place in the body It. For example, and as shown in Fig. 7 the resistance element 53 is placed edgewise in the annular space 29 in the body l6 and is spaced from the annular wall 23 by spaced strips 555 disposed between the resistance element as and the outer cylindrical surface of the annular wall 23 and in register with the slots il in the annular wall 22. A pressure distributing sheet 53 is placed on the outer surface of the resistance element 53 and in register with each strip 96 and a wedge device 18 is placed in each slot ll to urge the sheets 97, the resistance element 63 and the strips 95 toward the annular wall 23. The flanges 84 and 85 of the spring part it? are disposed against the sheet 91 and the channel part 80 is disposed in the slot H and so that the inner surface of the wall 94 bears against the spring finger 85. While the wedge devices if-3 are in the slots H but before the parts 13 and 5? of the wedge devices 3'3 are pressed fully down in the body IS the resistance element 63 is adjusted in the body 16 so that predetermined parts of the resistance element '53 are in register with predetermined lugs 59 on the upper edge of the wall 23. The predetermined parts of the resistance element 63 may be in each case a particular turn of Wire on the resistance element 63. With the wedge devices 18 all lightly in place and while the wedge devices 78 are operating to lightly hold the resistance element 63 in place the resistance element may be precisely adjusted in the body is to'bring the desired points on the resistance element 63 in register with the lugs 59 by inserting wedge sticks 98 in the notches 76. The wedge sticks 98 are constructed along the lines of the wedge sticks 8i and are thicker than the strips 96. When a wedge stick 58 is forced downwardly in a notch ii] the wedge stick $38 bulges a portion of the resistance element 83 outwardly of the wall 23. It will be seen that the point of bulge of the resistance element 83 is between two points at which the resistance element 63 may be lightly held by means of the wedge devices I8 and-that by applying pressure to the resistance element 63 through operation of the wedge stick 98 the resistance elemnt 03 may be moved relative to the lugs 09 to bring a particular point or turn of wire on the resistance element 63 in register with a predetermined lug 69 on the wall 23. After the wedge sticks 98 are operated to cause the required adjustment of the resistance element 03 the parts I9 and 80 of the wedge device I8 are forced downwardly in the body IE to develop more spring pressure in the spring finger 80 and apply sufficient pressure to the resistance element 63 at the point required to hold the predetermined point of the resistance element 63 against movement relative to the lug 33 on the wall 23. After the precise adjustment of the reistance element 03 has been made the wedge sticks 8i8l are applied to the other parts of the wedge device I8. The wedge sticks 3IBI are applied between the inner surfaces of the Walls 92 and 93 of the channel part 80 and the outer surfaces of the walls 02 and 83, respectively of the spring part I9 and operate to force the walls 92 and 93 of the channel part against the side walls of the slot II to maintain the Wedge device I8 against accidental or other undesired movement in the slot I I Since the wedge sticks 8I-0I also bear against the walls 82 and 83 of the spring part 39 they help to hold the spring part I9 in required position in the channel part 80. After the wedge sticks 8I8l have been driven downwardly in the channel part 80 to required position any portions of the wedge sticks SI-BI extending above the top of the channel part 80 may be removed by breaking off the unrequired portions of the wedge sticks 8 I8 I The serrations on the wedge sticks BI facilitate breaking the wedge sticks at the required points. The sheet 91 is apertured at 90 as shown in Fig. 9 to allow the tongue 90 to project therethrough and into engagement with the Wall 23 to keep the lower end portion of the spring part I9 in required position in the lower end portion of the channel part 80.

The resistance elements 60, 02 and 63, when mounted in the body I6 as shown in Fig. 1, follow in general the forms of the annular spaces in which they are disposed and have edge portions projecting upwardly out of the spaces so that edge portions of the resistance elements may be frictionally engaged by wiper contacts I00, IOI, I02 and I03, respectively. In some cases in potentiometers constructed along the general lines of the potentiometer shown a plurality of resistance elements are mounted in the same annular space in the body I0, the resistance .elements mounted in the annular space being arranged in series and so that an end of one resistance element is in register with an end of another resistance element. At points where one end of a resistance element is in register with another end of the resistance element or where one end of a resistance element is in register with an end of another resistance element track plates I04 and I05 are provided. The. track plates I04 and I05 are disposed edgewise in the annular space and so that they cooperatively embrace the resistance element ends and form in effect a bridge to support the free end portion of the wiper contact when the wiper contact is passing from one resistance element end to another. The track plates I04 and I05 are held in place by a bar I00 and spring clips I07, the bar I06 being disposed between one of the track plates and an annular wall of the body andthe spring clips I0! being disposed between the other track plate and another annular wall in the body and which cooperates with the first-mentioned wall to formthe annular space in which the track plates are disposed.

The wiper contacts I00, IOI, I02 and I03 are supported on arms I08, I09, H0 and III, respectively, the wiper contacts being secured to the arms by means of screws H2 or other suitable fastening means. The arms I03, I09, H0 and I I I are mounted in spaced relation on the upper portion II3 of the shaft I3 so that upon relative rotation of the shaft I3 and body I6 the wiper contacts I00 to I03, inclusive are frictionally moved over edge portions of the re.- sistance elements.

Eacharm' I00 to III, inclusive, comprises a plate portion II4, an arm portion H5 which is channel shaped in cross-section and a body portion I I6. The body portion H6 as shown in Fig. 7 is apertured to receive the shaft I3 and is made like an incomplete ring so that it may be sprung open to accommodate the shaft l3 and is provided with inwardly extending spaced projections III to frictionally engage the shaft I3. An upwardly extending flange H8 is provided on the outer edge portions of the arm portion II 5 and the body portion I I0. A mounting plate I I9 is provided for each arm I03 to III, inclusive. The mounting plate II 9 has a flanged annular body portion I20 and a flanged arm portion I2I,

I the body portion I20 being constructed to fit over the body portion H6 and the arm portion I2I being constructed to fit over the arm portion II5 above described. The body portion I20 is provided with inwardly extending lugs I22 to engage in a set of spaced grooves I23 formed in the shaft I3 and extending longitudinally of the upper portion of the shaft I3. Each arm I08 to I I I, inclusive, is releasably secured to its mounting plate I I9 by a bolt or other suitable fastening means I24 and means which will be later described are provided to permit and facilitate adjustment of each arm relative to its mounting plate H9.

The arms I08 to III, inclusive and their mounting plates II9 are arranged in stack formation as shown in Fig. 8 and with washers I25, I20 and I2! on the upper portion of the shaft I3, the washers I25 to I2I, inclusive, having inwardly extending lug portions such as I28 lating tube I29 which is mounted on the shaft I3,the lower end of the tube I29 resting on the upper end of the bearing I5. The insulating tube I29 provides an insulating support for spaced conducting rings I30, I3I, I32 and I33 carrying respectively collector rings I34, I35, I30 and I3! of good electrical conducting material. Each collector ring I34 to I31, inclusive, has an annular groove I38 formed in its outer surface and is securely mounted on its associated conducting ring. Each conducting ring I30 to I33, inclusive, is provided with an inwardly extending projection I39. The insulating tube I29 is provided with spaced longitudinal passageways I40 and into which the projections I39 extend. The passageways I40 form receptacles for insulated wires I4I which are led from the wiper contacts to the conducting rings.

Each collector ring I34 to I31, inclusive is in frictional engagement with an individual pair of wire members I42 and I43 shown in Fig. 15.

The wires I42. and I43 are attached to and extendirom a conducting plate I44 and cooperate to embrace the grooved portion of the collector ring, the wires I42 and I43 being bent to follow the curvature of the collector ring. The bent wires I42 and M3 are wrapped with wire, the wire I42 having a wrapping of wire I45 and the wire I53 having a wrapping I46 in frictional engagement with the grooved portion of the collector ring. The conducting plate I44 is apertured to accommodate an eyelet I4? which is secured to. the conducting plate I44. The wire wrappings I45 and I46 are led through aper tures I48 in the plate I45 and are brought over the top of the eyelet I4! and are connected to the eyelet I47. The lower portion of the eyelet I4! as shown in Fig. 8 is secured by means of solder or in any other suitable manner to the top of a helical spring I 49, the lower end of which is secured to the flanged bushing 59. The plate I44 and the eyelet M! are therefore supported by a helical spring I46 extending upwardly from a fixed member (the bushing 59) and while operable to move relative to the collector ring will by virtue of the he ical spring I49 be constantly urged to normal position. Extended through the eyelet I4! and secured thereto is a conductor wire I56 which extends downwardly through the spring I 49, the bushing 56 and an internally threaded pipe Ii from the lower end of which the conductor wire I58 is led and connected to the terminal 54. The pipe I5! has threaded connection with the lower threaded end of the bushing 56 and is provided with a screwdriver slot I52 at its lower end to facilitate connecting of the pipe I5! to the bushing 53.

The plate I4 is provided with a downwardly extending leg I53 which is engageable with the wall to limit extent of movement of the plate I44 outwardly relative to the collector ring.

In some cases the conductor wire I56 may be led from the pipe I5! directly to a terminal, not shown and, not mounted on the body I6. Each wiper contact I65 to I63, however, has electrical connection with some remote point and the course of the connection may be understood by a consideration of the connection shown for the wiper contact I 63. The conductor of the insulated wire I4! as shown in Fig. 'I is connected to a heel portion I54 of the wiper contact I 63 and is then snubbed around a post I55 supported on the arm- III. The wire I4! is extended from the post I55 throu h the space between the arm III and its mounting plate I!!! and then downwardly between the shaft !3 and the body portion I I6 of the arm I I I and through a passageway I45 in the insulating tube I 26 to a projection I39 on the conducting ring I 36. The conductor of the insulated wire I4! is connected to the projection I36 on the conducting ring I 33. The collector ring I3? on the conducting ring I 33 is in frictional engagement with the Wire wrappings I45 and I56 which are electrically connected to an eyelet I4? on a plate I44. A wire I56 connected to the eyelet It! extends downwardly through a spring I46, a bushing 59 and a pipe I5! and outwardly through the lower portion of the body I6 and may be connected to a terminal 54 mounted on the lower portion of the body I 6 or may be led to. any remotev point required.

End orother predetermined portions of the resistance elements may be electrically connected to. terminals 54 on the lower portion of the potentiometer by means of lead wires such as the lead wire I56 shown in Fig.. 8.. In this case the lead wire I56 is connected to a predetermined turn of. resistance wire on the resistance element 66 and is led downwardly through the annular space 29 in the body of the potentiometer and through the lower wall of the body It by way of an opening I5! formed by knocking out the closing wall of one of the knockouts 48. It is obvious from a consideration of Fig. 8 that the lead wire I56 may be attached to a terminal or to any other suitable point after the lead wire I56 is extended through the lower wall of the body f the potentiometer.

Relative rotation of the shaft I3 and the body I6 may be readily accomplished by connecting a rotating member, not shown, to the stub I58 on the shaft I3 while the body I6 is held stationary, or the body I6 may be rotated by any suitable means while the shaft I3 is held stationary. Relative rotation of the shaft I3 and the body will cause relative rotation of the wiper contacts I66 to I63, inclusive, and the resistance elements to 63, inclusive.

The cover I I as shown in Fig. 2 is a cup-shaped member removably mounted in inverted position on the body I 5 and constructed to fit over the upper portion of the body I6 and screw threadably engage the screwthread 3! on the body I6. Rib-like embossings I59 are provided on the outer surface of the cover I! to facilitate manual application of the cover I! to the body I6. Recesses I60 with tubular inserts I 6! mounted therein are provided on the cover I! to facilitate tightening or loosening the cover I! by means of a suitable tool such for instance as a wrench device. Extending downwardly within the cover I! and located in the central portion thereof is a pin I62 which is rotatably supported in an apertured disc I63 supported in an undercut recess I64 in the under surface of the cover II. When the cover I! is applied to the body I6 the pin I62 engages a ball I65 mounted in the upper portion of the shaft I3 and the ball I65 and the pin I62 in cooperation serve as an end thrust bearing for the shaft I3 to keep the bearing I5 on the shaft I3 seated in the seat bearing I4. The pin I62 also insures that the central portion of the cover I! will not engage the upper end of the shaft I3 and on which a nut I66 and a stack of washers I6! are mounted to hold the stacked portions of a the wiper arms, mounting plates and associated washers in place on the shaft I3.

The ball I65 is located in a well I63 formed in the upper end portion of the shaft I3 and rests on a plunger I 69 supported on the upper end of a helical spring IIII located in the well I68. A ring "I sprung into an annular indentation H2 in the shaft 13 and positioned above the ball I 65 maintains the ball I65 in the well I68. When the pin I62 on the cover I! engages the ball I65 and the cover I! is being moved to its normal position on the body I6 the ball I65 is pressed away from the ring I I! and pressure is developed in the spring III]. The thrust of the pin I62 on the ball I65 and the pressure developed in the spring I!!! keeps the conical bearing I5 on the shaft I3 seated in the seat bearing I4.

As previously mentioned with regard to the wiper contact supporting arms I68 to III, inclusive, means are provided to permit and facilitate adjustment of each arm relative to its mounting plate H9. The means provided for the purpose are shown in detail in Figs. 16 to 19, inelusive.

As shown in Figs. 7 and 16, the flanged arm portion I2! of the mounting plate III! has an apertured and sloped embossing I14 bulged upwardly in the region of location of the bolt I24. The bolt I24 is rotatably supported in a spiral threaded adjustment member I15 which is rotatably supported in the aperture in the sloped embossing I14. The spiral t readed adjustment member I15 has a central bore I18 dimensioned to accommodate the shank portion of the bolt I24 and has a recessed head portion I11 formed to receive the head of the bolt I24. The outer surface of the head portion I11 is formed to make it adaptable to be engaged by a wrenc not shown, to facilitate rotation of the spiral threaded adjustment member I15. The lower end of the spiral threaded adjustment member I15 is enlarged in diameter to provide a disc portion I18 on the lower surface of which is formed a spiral thread I19 adapted to engage embossings I89 formed on the upper surface of the arm portion II of, for instance. the arm III. The embossings I88 form, in effect, portions of a screw thread of the same pitch as the spiral thread I19 and are located between one side of the arm portion H5 and an elon ated central aperture I8! formed in the arm portion H5. The disc portion I18 extends at an angle relative to the upper surface of the arm portion I I5, the upper surface of the disc portion I18 being in enga ement with the under surface of the sloped embossing I14 and the spiral thread I19 being in engagement with the embossings I88 on the arm portion H5. When the spiral threaded adjustment member I is rotated, the arm portion II 5 is laterally moved by virtue of the spiral thread I19 and the embossings I80, the direction of movement being determined by the direction of rotation of the piral threaded adiustment member I15. When the arm portion H5 is thus moved, the arm III rotates relative to the shaft 13 and causes the wiper contact, such for instance as the wiper contact I93, to move along the resistance element 63. By suitable operation of the spiral threaded adjustment member I15, precise adjustment of a wiper contact may be made to bring the wiper contact to a particular predetermined turn of wire on the resistance element when the arm supporting the wiper contact is brought to a predetermined position. Also, by suitable operation of the spiral threaded adjustment member I15, a wiper contact may be adjusted so that it extends in parallel relation with an engaged turn of wire or in an ular relation with an en aged turn of wire on the resistance element served by the wiper contact.

The bolt I24 is equipped with a nut I82 which r is used in cooperation with the bolt I24 to hold the arm portion I I5 within the space defined by the flanged arm portion I 2| of the mounting plate H9. The nut I82 comprises a block-like body I83 terminating at its lower end. as shown in Figs. 17 and 19, in a rectangular enlarged base portion I84. The nut I82 is internally threaded to receive the threaded end of the bolt I24 and the block-like body I83 is dimensioned to fit the smaller dimension of the elongated aperture IBI in the arm portion II5. When the nut I82 is applied to t e bolt I24, the block-like body extends upwardly through the aperture I8I in the arm portion I I5 and when the bolt I24 is tightened, the base portion I84 of the nut en ages the under surface of the arm portion I I5 to hold the arm portion II5 against the mounting plate H9.

The corners of the block-like body portion I83 of the nut I82 are provided with grooves I85 to receive a spring wire clip I86 which extends d es- Cir E5 resistance element to hold the resistance element] onally across portions of the elongated aperture I8I and over portions of the upper surface of the arm portion II5, the function of the spring wire clip I86 being to allow slight downward movement of the nut I82 when the bolt I24 is turned counter-clockwise to slightly release the arm portion II5 from tight pressure against the mounting plate H9 and still prevent the nut I82 from dropping through the elongated aperture I8I in the arm portion I I5.

The spiral threaded adjustment member I15, as shown in Fig. 16, is equipped with pins I81-I81 which extend through transverse apertures I88, shown in Fig. 18, formed in a neck portion I89 of the spiral threaded adjustment member I15, the neck portion I89 being defined by a flange I90 and a shoulder I9I formed on the spiral threaded adjustment member I15. The pins I81 extend a sufficient distance into the bore I16 of the spiral threaded adjustment member I15 to prevent undue'complete upward withdrawal of the bolt I24 from the spiral threaded adjustment member I15; the pins I81 however do not normally engage the bolt I24. The outer ends of the pins I81 are reduced in diameter to extend into apertures formed in a diametrically divided two-part retainer ring I92 which is located in t e neck portion I89 and bears against the shoulder HM and 'the under surface of the flange I98 on the spiral threaded ad ustment member I15. The two parts I93 and I94 of the retainer ring I 92 are held clamped about the neck portion I89 of the spiral threaded adjustment member I15 by means of a snap spring device I95 which almost encircles the retainer ring I92 and rests in grooves I96 formed in the outer surfaces of the two parts I93 and I94 of the retainer ring I92. The retainer ring I92 in addition to holding the pins I81I 81 against outward movement also serves as a retainer ring for the spiral threaded adjustment member I15 and holds the spiral threaded adjustment member I15 against downward movement in the flanged arm portion I2I of the mounting plate I I9, washers I91 being dis- 4 posed between the under surface of the retainer ring I92 and the upper surface of the flanged arm portion I2I.

The means comprising the spiral threaded adjustment members I15 for adjusting the wiper contact supporting arms are of considerable advantage in a potentiometer of the type shown and described since through suitable operation of the spiral threaded adjustment members I15, the

wiper contacts may be precisely set relative to particular turns of wire on the resistance elements after the resistance elements have been mounted in the body and the wiper contacts and supporting arms have been mounted in place. To make a precise adjustment of a wiper contact, it is only necessary to loosen the bolts I24 and turn the spiral threaded adjustment member I15 in the required manner to make the arm portion I I 5 rotate relative to the shaft 13 to the required extent to bring the wiper contact to the required position relative to the particular turn of resist ance wire and then tighten the bolt I24.

What is claimed is:

1. In an electrical device in which a wiper contact, engages a resistance element, a body, a pair of spaced walls insaid body and defining a space in said body to receive the resistance element and a spring wedge shaped device in the space V defined by said walls-and operating against one of said walls and applying spring pressure to the in place in said body for engagement by the wiper contact.

2. In an electrical device in which a wiper contact engages a resistance element, a body, a pair of concentric spaced walls in said body and defining a space in said body to receive the resistance element and hollow spring wedge shaped means with wedge sticks therein disposed in the space in said body and spaced along the resistance element and applying spring pressure against said walls and at spaced points along the resistance element and operating to hold the resistance element at spaced points and in position in said body for engagement by the wiper contact.

3. In an electrical device in which a resistance element is supported for engagement by a wiper contact spring, wedge shaped means for supporting the resistance element at spaced points along the resistance element and a body for holding the resistance element and said spring wedge shaped means, said body comprising a lower wall, spaced walls extending upwardly from said lower Wall and cooperating with each other and with said lower wall to define a space in which the resistance element and said spring wedge shaped means are located and spaced slots formed in at least one of said spaced walls and extending downwardly in and opening into the space defined by said walls and providing accommodations for said spring wedge shaped means.

4. In an electrical device in which resistance elements are concentrically arranged and supported in spaced relation for engagement by wiper contacts, a body comprising a lower Wall, recesses formed in said lower wall to provide knock-outs through which wires can be extended, spaced walls extending upwardly from said lower wall and cooperating with said lower wall to define annular spaces in said body to accommodate the resistance elements, spaced slots and spaced notches formed in said spaced walls and opening into the annular spaces in said body, said notches being not in register with said slots, spring wedge shaped means supported in said slots and cooperating with said spaced Walls to hold the resistance elements in place in said body and wedge shaped stick means disposed in said notches and in engagement with portions of the resistance elements and operating to bulge portions of the resistance elements from the walls in which said notches are formed.

5. In an electrical device comprising a body, a resistance element supported in the body and a wiper contact in engagement with the resistance element, an arm supporting the wiper contact, a shaft mounted in the body and supporting said arm said shaft being rotatable relative to the body, a conducting ring carried by said shaft, a grooved collector ring supported on said conducting ring, means electrically connecting the wiper contact to said conducting ring, flexible conductors disposed in the groove in said grooved collector ring and embracing said collector ring, a helical spring secured at one end and mounted in the body, said helical spring extending into P register with said grooved collector ring, an eyelet supported on said helical spring and in register with said grooved collector ring, said eyelet being electrically connected to said flexible conductors and a conductor wire extending through said helical spring and electrically connected to said eyelet.

6. In an electrical device in which a card-like electrical element is mounted in a body, spaced walls in the body defining a space in the body for accommodation of the electrical element, a channel member disposed between one of the spaced walls and the electrical element, a spring fingered member nested in said channel member and cooperating with said channel member to apply spring pressure to a predetermined point on the electrical element and urge the electrical element toward another of said spaced walls with sufficient pressure to hold the electrical element in place in the body and wedge stick means disposed in said channel member and bearing against said channel member and said spring fingered member to hold said spring fingered member in said channel member.

LEON N. HAMPTON. ORWAR. S. A. MESCH. CHARLES V. OBST.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 733,610 Yates July 14, 1903 1,577,048 Thomas Mar. 16, 1926 2,403,989 Mallina July 16, 1946 2,419,952 Konicek et al May 6, 1947 

